Power transmission belts, for example V-belts and ribbed V-belts, are well known (See: Wake, N. C., et al., "Textile Reinforcement of Elastomers", Applied Science Publishers, Englewood, N.J., 1982). Such power transmission belts typically comprise rubber impregnated fabric layers disposed on the belt's innermost and outermost circumferential surfaces, and a layer of a masticated rubber/staple fiber mixture and a layer of circumferentially disposed reinforcing cord being sandwiched therebetween. The reinforcing cord or "stiff cord" is typically made from an adhesive impregnated, multi-filament yarn. Exemplary yarns include filaments of nylon, polyester, and rayon, polyester being preferred because of its superior properties.
Generally, these belts are made by laying up the above-mentioned layers, in an inverted order, on a drum. First, a layer of rubber impregnated fabric is laid on the drum. Then, the reinforcing cords are laid up. Next, a layer of masticated rubber/staple fiber is laid up. Finally, a second layer of rubber impregnated fabric is applied to the construction. The foregoing is then vulcanized, thereby forming a "large tube". From this tube, individual belts are cut.
One problem with this type of belt is "cord pop-out". "Cord pop-out", or fraying of cord from the belt's cut edge, seriously diminishes the belt's useable life span because the loss of cord from the belt accelerates wear on the belt leading to its ultimate failure. Cord pop-out and situations which lead to cord pop-out can arise during manufacture and use of the belt. In manufacture, when belts are cut from the tube, the cord or the yarn in the cord can be stripped away. In use, as the belts leaves the sheave, the cord or the yarn may "pop-out" of the belt because of the reduction of lateral compressive force on the belt.
"Cord pop-out" is such a serious concern that the reinforcing cords or "stiff cords" are impregnated with an adhesive to facilitate inter-filament bonding. Inter-filament bonding within the yarn and cord reduces the possibility of individual filaments popping from the belt and begin fraying from the belt. Typical adhesives for inter-filament bonding include isocyanate systems which are normally applied to the cord in a solvent carrier. The solvent/isocyanate systems is necessary so that the isocyanate penetrates in between the filaments of the yarn and thereby facilitates inter-filament bonding (See: Wake, W. C., Ibid., pg. 89-90). These solvents, however, pose significant environmental problems (See: Wake, N. C., Ibid.). These adhesive systems for inter-filament bonding should be differentiated from the resinol-formaldehyde-latex (RFL) systems (aqueous based systems) which are applied to the cord. The RFL systems enhance and promote adhesion of the cord to the surrounding rubber.
Accordingly, there is a need to find a way to prevent cord pop-out in power transmission belts without the use of the solvent carrier for the isocyanate adhesive system.
There is also a need to develop new cord reinforcement products for the rubber goods industry. The rubber goods industry includes any rubber product which uses a reinforcing cord, e.g. power transmission belts, conveyor belts, tires, and the like. Polyester (i.e. polyethylene terephthalate) reinforcement cord is a reinforcement product of choice in most of those applications because of its strength and dimensional stability, but polyester cord suffers because of its inherently poor adhesion to rubber. Consequently, adhesives systems have been devised that overcome the poor adhesion. Work, however, continues to improve the adhesion of polyester to rubber.